The invention generally relates to an improved catheter and a method for treating conditions of the brain area and, more particularly, to an improved ventricular catheter adapted for placement in a subdermal tunnel, and a method for sensing physical parameters in the skull area with a ventricular catheter and placing the catheter in a subdermal tunnel in an improved manner to expedite the subdermal placement procedure and to reduce the risk of infection.
Head injuries, other pathologic neurological disorders and systemic diseases have been shown to cause acute swelling of the brain or an increase in the volume of cerebral spinal fluid (xe2x80x9cCSFxe2x80x9d). The so-called xe2x80x9cclosed-boxxe2x80x9d cranial vault restricts the amount of increase that can be tolerated before the increase in intracranial pressure poses a danger to the patient. The contents of the cranial vault are essentially non-compressible and comprise approximately 80% brain, 10% CSF and 10% blood. An increase in one of the components requires a decrease in one or both of the others to accommodate the change. An increase in the brain or CSF may result in undue pressure on healthy tissue resulting in temporary or permanent disability to the patient. Intracranial pressure sensors, catheters and shunts have been developed to monitor and manage the treatment of these patients, either through the recording and manipulation of information from the sensor or through the shunting mechanism from a catheter in the ventricle.
The intracranial pressure monitoring devices are introduced into the brain through an access hole in the skull. When placement in the ventricle is desired, the opening is appropriately close to the anterior horn of the lateral ventricle and the catheter and/or sensor is inserted through the access hole into the ventricular space. The pressure sensor in the distal end of the catheter conducts information via a cable in the catheter to an external monitor. Simultaneously, fluid may be drained from the ventricle and collected in an external drainage bag or system to relieve pressure. The monitoring and management of the patient may be hours or many days, typically five to ten days.
Because of the extended amount of time that the ventricular catheter must be positioned in the patient, and because of the invasive nature of the procedure, another consideration is the increased risk of infection of brain tissue by pathogens entering through the skull opening or access hole. The presence of a direct pathway through the skull access hole from an outside environment directly into the brain ventricle causes a substantial risk of infection. To reduce this risk, a catheter placement technique referred to as subdermal tunneling has been developed.
In the prior fluid-filled pressure sensing catheter approach, a foil strain gauge or rosette of strain gauges is located at the proximal end of the catheter or within an apparatus outside of the catheter. The distal end of the catheter is inserted into the cranium and receives fluid from the cranium in a lumen extending completely through the catheter to the proximal end. The fluid pressure in the catheter lumen acts on the surface to which the gauges are attached and the gauge or gauges provide an electrical signal representative of the strain in the surface which can be correlated to pressure in the cranium.
In this fluid-filled catheter approach, traditional or forward tunneling under the scalp is typically used. A surgeon makes an incision, or first opening, in the patient""s scalp exposing a portion of the skull overlying a ventricle of the brain. Subsequently, a twist drill access hole is formed through the skull exposing the interior of the cranial vault. Next, the distal end of the fluid-filled catheter is inserted into the twist drill access hole after which the proximal end of the catheter is connected to a sharp pointed tunneling instrument, such as a trocar or needle. The trocar is inserted under the scalp at the point of incision just proximal of the skull access hole and is advanced through the scalp to form a subdermal tunnel of typically five or more centimeters. The tunneling instrument is pulled through the tunnel to exit the scalp at this exit opening. The proximal end of the catheter, which is attached to the end of the trocar, is also pulled through the tunnel and is then pulled taut in the tunnel. The surgeon then sutures the scalp over the skull access hole and over the tunnel entrance and exit thereby sealing the skull access hole and the scalp openings.
The diameter of the tunnel is kept as small as possible and is just larger than the diameter of the catheter that must be threaded through the tunnel. The small diameter of the tunnel contributes to lowering the risk of infection. It has been found that the subdermal tunnel technique substantially decreases the risk of intracranial infection by providing an elongate tunnel through which pathogenic organisms would have to pass before they could enter the cranial vault through the skull access hole. There is thus no direct pathway for contamination to enter the access hole. The tunneling technique has proven very successful.
One of the drawbacks of a fluid filled catheter is that the pressure head created by the fluid column in the catheter must be subtracted from the pressure readings to get an estimate of the actual CSF pressure within the brain ventricle. The common use of oscillating beds in head injury cases further complicates this problem by causing fluctuations in the fluid column. To solve the pressure measurement problem associated with fluid filled catheters, transducer tipped catheters that include sensors, typically strain gauges or optical sensors, placed within the catheter""s distal end were developed.
Transducer tipped catheters used in ventricle pressure sensing have a transducer of an electrical or optical nature located at the distal tip of the catheter, that is placed within the cranium of the patient. There is an elongate shaft connecting the catheter""s distal end with its proximal end. The proximal end of the catheter includes a connector that is used to connect the internal optical or electrical conductors to another connector located on an intermediary cable or directly on an instrument for displaying the pressure sensed or other physical parameter that has been sensed to the physician and nursing staff. Such connectors not only interconnect the signal communication line, but also provide a physical device that locks the two connectors together to apply the necessary pressure to force the internal conductor of one connector into good signal contact with the internal conductor of the other connector, and so that they do not become inadvertently disconnected. Because of this locking device and other design parameters of prior connectors, they have been too large to fit within the small subdermal tunnel discussed above. Therefore, transducer tipped catheters have been reverse tunneled.
Reverse tunneling is similar to traditional tunneling except that the trocar is used to puncture the scalp at a location distal of the skull access hole and is tunneled towards the skull access hole from the distal location. After formation of the subdermal tunnel, the distal end of the catheter, which is smaller than the connector, is inserted into the second scalp opening (remote from the skull access hole) and pulled through the tunnel to the scalp opening adjacent the skull access hole. The needed length of catheter is pulled through the tunnel in the direction of the skull access hole up to the point that the large connector or other device mounted to the catheter cannot be pulled farther. The large connector will either come into contact with the distal scalp opening or, if partially pulled into the tunnel, will be prevented from further advancement due to its larger size as compared to the smaller diameter of the tunnel. The physician then positions the distal end of the catheter in the ventricle or other cranial location as desired and the catheter is fixed in the desired in-dwelling position in the skull access hole. The excess catheter length is then pulled in the opposite direction through the tunnel in the direction of the distal scalp opening to make the catheter shaft taut, and the suturing of the scalp over the access hole and the tunnel openings may then occur.
An example of such a transducer tipped catheter and the above-described technique of tunneling is shown in U.S. Pat. No. 5,312,357 to Buijs et al. FIGS. 2a through 2f in general show the prior method described above. FIGS. 8a through 8h also show the prior method described in addition to showing the typically large proximal end connector of such catheters.
Although the use of ventricular catheters having a sensor or sensors located at their distal tips is advantageous in that such catheters provide direct readings of pressure or other physical parameters in the cranial area, the reverse tunneling technique required to use such catheters is disadvantageous in that the distal end of the sensor equipped catheter must pass through the subdermal tunnel thereby exposing the distal tip to possible contamination with foreign matter, pathogens, or other infectious agents. Any pathogens that may be introduced into the brain through the skull access hole may create a subcranial infection with severe adverse consequences for the patient. Thus, great care must be taken with this prior tunneling method and as a result, it is substantially less desirable than the traditional tunneling method.
In addition, the above-described reverse tunneling method has been found to make it more difficult in many cases to locate the distal tip of the ventricular catheter in the proper position in the ventricle of the patient. When the shaft of the catheter is already located in the subdermal tunnel, the remainder of the catheter shaft between the tunnel and the distal tip is restrained in its movement due to the proximal end being located in the tunnel. Even though the catheter has been threaded through the tunnel to provide as much slack as possible for the distal end of the catheter, the fact that the proximal end of the catheter is held firmly in a fixed position can act as a restraint on the physician""s ability to maneuver the distal tip of the ventricular catheter during its placement in the patient""s ventricle. As is well known to those skilled in the art, it takes a large amount of skill under the best circumstances to accurately place the ventricular catheter in the correct position in the patient""s ventricle without causing excessive trauma to the patient. The added problem of having to deal with a restrained proximal end of the ventricular catheter requires an even greater level of skill. The large size of the connector at the proximal end of the ventricular catheter has made the above problems occur. Increasing the tunnel size so that the proximal end connector could itself be pulled through the tunnel would defeat the antiinfection purpose of the tunnel.
Furthermore, the above-described tunneling technique occurs before placement of the distal end of the catheter in the patient""s cranium, thus delaying the stabilization of the patient. Using two catheters, one to first stabilize the patient while the second more permanent catheter is being tunneled, is undesirable due to exposing the patient to the increased trauma of two catheters and two access holes. It would be preferable to be able to immediately relieve excess pressure on the patient""s brain with the same catheter that will be tunneled in the subdermal tunnel for location of the catheter shaft and thus lower the trauma to the patient.
Another area in which improvement is desired is in the process of threading the catheter through the subdermal tunnel. In some cases, needle-type devices are used to form the tunnel and as a result, tissue and blood are encountered by either the proximal end or the distal end of the ventricular catheter depending upon whether the catheter is traditionally or reverse tunneled. It would be desirable to insulate the ventricular catheter from these possible contaminants as much as possible. Further, any device used in the tunneling should assist in threading the catheter through the tunnel so that the catheter is not crimped, stretched, or kinked in any way. As is well known, crimping, stretching, or kinking can damage internal components of the catheter, such as optical fibers or electrical conductors, making the catheter inaccurate or unusable. Various approaches at solving these concerns have been attempted, including a notch formed in a guide type device located in the tunnel and in which the catheter is threaded. However, the notch is open and may accumulate contaminants.
Hence those skilled in the art have recognized a need for a catheter having a sensor or sensors located at its distal end, and that is small enough so that it may be placed in a subdermal tunnel but need not be first located in the tunnel prior to location in the patient""s cranium. In addition, a catheter that can be tunneled in this way and that is able to both measure a biological parameter or parameters within the cranium and provide for drainage of CSF when required, and having a small outer diameter for reduced trauma to the patient is needed. Further, it is desirable that such a catheter be able to accept a stylet for use in placing the catheter in the correct position in the cranium, yet provide means to protect the internal lumen or lumina of the catheter when exposed to the threading process through the tunnel. A need has also been recognized for a catheter and method whereby a single catheter may be used for immediately stabilizing the patient and may also be used for long term use, thereby obviating the need for two catheters and for two access holes. Further, a need has been recognized for a method of placing the catheter in the cranium of the patient first so that the patient may be stabilized as soon as possible, and then providing a tunneling step for more long term location of the catheter shaft in a subdermal location. The present invention satisfies these needs and others.
The present invention provides a catheter having proximal and distal ends, including a drainage lumen and a distal sensor for sensing a selected physical property or properties in the cranium of a patient and for transmitting signals representing those properties in either optical or electrical form to a miniaturized proximal connector at the catheter""s proximal end. The miniaturized connector is configured to have a size such that it can be pulled through a subdermal tunnel by a tunneling instrument so that a traditional or forward tunneling technique may be used with the sensor-tipped catheter. A skull access hole that provides access to a ventricle of a patient""s brain is formed, the catheter inserted in the access hole by the physician, and then the adjacent subdermal tunnel is formed. The proximal end of the catheter is then pulled through the subdermal tunnel while the distal end of the catheter remains in position in the access hole.
In another aspect, the drainage lumen of the catheter includes multiple ports in the distal end for receipt of CSF and includes a drain port in the proximal end for drainage to a collection apparatus. The drain port and lumen also serve to receive a stylet for use in stiffening the catheter for initial insertion of the distal end of the catheter through the access hole and into the ventricle of the patient. The drainage/stylet lumen is terminated in the intermediate portion of the catheter body so that fluid must leave the lumen through the drainage/stylet port. This prevents fluid internal to the catheter from reaching the proximal end of the catheter where the miniaturized connector is located.
Generally, the present invention contemplates a method for placement of a catheter in a patient by first placing the catheter through an access hole created in the cranium, locating the catheter in a desired position within a ventricle of the brain, and then securing the external part of the catheter shaft within a subdermal tunnel in the patient""s scalp. In more detailed aspects, such a catheter may be used in measuring intracranial fluid characteristics by forming an incision exposing a region of the skull over a ventricle of the brain; creating a twist drill access hole through the skull having fluid pressure; placing the distal sensor-equipped end of the catheter into the twist drill access hole; attaching the proximal end of the catheter to a tunneling instrument; using the tunneling instrument to form a subdermal tunnel from the twist drill access hole to a point distal of the access hole, and forming a second opening with the tunneling instrument at the distal location; removing the tunneling instrument through the second opening and pulling the attached catheter taut through the second opening; connecting the drainage lumen to a fluid collection apparatus; and connecting the miniaturized connecter mounted at the proximal end of the catheter to an intermediate connector and thereby sensing CSF characteristics transmitted from the sensor equipped catheter.
Thus the method and apparatus of the present invention provide a catheter having a sensor located at the distal tip of the catheter, having a drainage lumen, and a miniaturized connector at the proximal end of the catheter that allows the catheter to be forwardly tunneled, thereby eliminating the possibility of distal tip contamination that may occur with reverse tunneling techniques. The miniaturized connector also removes a restraint on the physician""s ability to properly locate the catheter in the patient in that the proximal end of the catheter is not placed in the tunnel prior to placement of the distal tip in the ventricle of the patient. In addition, the catheter of the present invention uses a single opening which serves to receive a stylet for placement of the catheter and as a drain port thereafter.
Direct placement of the distal end of the catheter in the skull access hole without the need to first thread it through a subdermal tunnel in accordance with aspects of the invention eliminates the possibility of contaminating the distal end with foreign matter or infectious agents, the primary weakness of the prior art, and permits the physician to accurately position the catheter in the patient without having the restraint of the proximal end of the catheter already located in the subdermal tunnel, also a weakness of the prior art.
Other features and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention, when taken in conjunction with the accompanying exemplary drawings.